Insulin and incorporation of amino acids into protein of muscle. Cellular amino acid levels and aminoisobutyric acid uptake.

The specific rotation, [o]", of soluble feather keratin was -430° at 250. The estimated probable error is + 45°. This was for a solution of protein concentration 3 mg./ml. The result of these experiments therefore clearly shows that the solution of soluble feather keratin has a large negative specific rotation that is of the same order of magnitude as that of collagen. The specific rotation of collagen (ichthyocol) in citrate buffer at 100, [o]1°, has been found by Cohen (1955) to be -350°+ 300. In general both collagen and the triple helical polypeptides poly-L-proline and poly-L-hydroxyproline exhibit a large negative specific rotation, [a]D, being in the range of -300° to -400° (Sasisekharan, 1961). On the other hand polypeptides of the a-helical form generally have a specific rotation, [m]D, in the range 0-50', whereas for wool (oc-keratin) [M]D is of the order of 500 to 00. In general, x-type proteins have a small negative rotation, whereas in the random-coiled or denatured form they have a specific rotation of the order of 1000. The fact that feather keratin exhibits a large negative rotation of -430° provides further evidence that it has a structure similar to that of collagen. The optical-activity data also support the triple helical structure of feather keratin.